The present invention relates to a copier, printer, facsimile transceiver or similar color image forming apparatus of the type recording a register mark or marks on a recording medium for registering the leading edges of images of respective colors to form a color image. More particularly, the present invention is concerned with such a type of image forming apparatus which does not need an exclusive cutter on cutting part of the recording medium carrying the register marks after image formation.
Generally, a color image forming apparatus of the type described includes a roll of recording medium, a writing device for electrostatically forming a latent image on the medium, a developing device having a yellow, a magenta, a cyan and a black developing unit, and a register mark sensor for sensing register marks recorded in black on the medium. It is a common practice with this type of apparatus to locate the register marks on the medium outside of an effective image area and adjacent to one side edge with respect to an intended direction of medium feed. The leading edges of images of respective colors are brought into register on the basis of the output of the register mark sensor. After the image formation, the register marks are not necessary and, therefore, cut off by a cutter.
A problem with the conventional apparatus described above is that a box or similar receptacle has to be disposed in or outside of the apparatus body in order to collect the register marks recorded along the side edge of the recording medium and cut off after image formation. Another problem is that not only a main cutter for cutting the medium in a predetermined size but also an extra cutter for cutting off the register mark portions are needed, resulting in a bulky and expensive construction.